This invention relates to a driving device for adjusting a vehicle part and to a method for operating a driving device.
Such a driving device comprises an electric drive for driving the vehicle part. The electric drive includes an output shaft for transmitting an adjusting force to the vehicle part. To this output shaft a first braking device is connected, which includes at least one permanent magnet element and is configured to provide a braking force for arresting the vehicle part in a currently adopted position.
In a driving device known from EP 1 940 012 A1 a braking device in the form of a so-called hysteresis brake includes a disk-shaped carrier element non-rotatably connected to an output shaft, to which a ring-shaped hysteresis element made for example of a soft-magnetic material is attached. The hysteresis element faces two permanent magnets on a stator. The hysteresis brake provides a braking force both at standstill and in movement of a tailgate, wherein the hysteresis brake can be switchable in order to reduce the braking force for example during a manual movement of the tailgate.
From FR 2 818 304 a drive for adjusting a vehicle part is known. The drive includes a braking device for holding the vehicle part in a set position.
In a driving device for pivoting a flap arranged on a body of a vehicle as it is known from DE 10 2005 030 053 A1 a braking device is provided, in which a brake disk is arranged on a shaft, which is brakingly acted upon by a brake element.
From EP 1 534 971 B1 a spring clutch actuated by a magnetic brake is known, in which a magnet is arranged in a position opposite a rotor disk. In the braking device described there a braking force is produced by inducing eddy currents.
From the prior art, there are also known so-called wrap spring brakes that use a wrap spring arranged in a brake pot. On introduction of a drive-side force the wrap spring is loaded to release an abutment with the brake pot, so that an output shaft can be driven without a large braking effect of the wrap spring. On the other hand, when a drive-side force is applied to the output shaft, the wrap spring is loaded in the direction of its abutment with the brake pot, so that the output shaft is braked and the output-side force is dissipated without the output shaft being adjusted.
Conventional braking devices of this type are expensive and have a considerable need for installation space. In addition, braking devices that utilize a friction for braking are susceptible to wear and possibly temperature-sensitive.